Shot Laplace was the 18th nuclear test of Operation Plumbbob, detonated on 8 September 1957 at 6 a.m. PDT from a balloon at 750 feet above Yucca Flat, shortly before sunrise. It was a Los Alamos Scientific Laboratory test of the so-called Fleegle device — an all-oralloy gun-type weapon, a design principle that by 1957 had become a rarity in American nuclear development, most weapons having long since moved to implosion. The shot produced 1 kiloton against a predicted yield of 1.5–2 kt. This Lookout Mountain Laboratory photograph — AEC-57-5833 — captures the fireball at the moment the caption describes directly: immediately after the detonation burned away the cables anchoring the balloon. The result is the Rope Trick Effect, clearly visible as dark streaks radiating outward from the fireball — the anchoring cables superheated and vaporized by the initial thermal pulse before the fireball itself had expanded to consume them. Laplace is named for the French mathematician and astronomer Pierre-Simon Laplace (1749–1827).